Elevation of total homocyst(e)ine in plasma is an independent risk factor for arterial occlusive disease in the general population, and is associated with vasculopathy and thrombosis in patients with homocystinuria. The pathogenesis of homocysteine-induced injury in vivo is not known, but in vitro experiments suggest that oxidative stress may be important. We induced hyperhomocyst(e)inemia in the atherosclerosis-susceptible C57BL/6J strain of mice by feeding a diet deficient in folate and choline and supplemented with methionine. This was compared with a control diet in a blind study of 5 weeks duration. Mice on the test diet had significantly elevated levels of total homocyst(e)ine in plasma, while lipid profiles showed no differences. Conjugated dienes in liver were higher on the test diet, as were relative levels of mRNA of glutathione peroxidase. No differences were observed for total and reduced glutathione levels, or levels of mRNA of glutathione S transferase, or glutathione reductase in liver. We have established a murine model of diet-induced hyperhomocyst(e)inemia. While the role of individual diet components needs further study, initial findings support the concept that oxidative stress may play a role in homocysteine- mediated injury in vivo.